<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      body{
        background-color: green;
      }
      .outer {
        width: 400px;
        height: 600px;
        background: red;
      }

      .inner {
        width: 50%;
        padding-bottom: 100%;
        background: blue;
        align-items: center;
        justify-content: center;
        position: relative;
      }
      style {
        position: absolute;
            left: 50%;
            top: 50%;
            transform: translate(-50%,-50%);
      }
    </style>
  </head>
  <body>
    <div class="outer">
      <div class="inner"></div>
    </div>
  </body>
  <script>
    var global = "global scope"; //全局变量

function checkscope() {

    var scope = "local scope"; //局部变量
    console.log(this)

    function f() {

        return scope; //在作用域中返回这个值
        console.log(this)

    };

    return f();

}

checkscope(); // 返回 "local scope"
5000       
checkin the book
function a() {
                                                                                                                                                                                                                                        
}                                                                                                                                                                                                                                                                                                                            
  </script>
</html>

 